Voltage controlled current source applications typically use a shunt resistor in series with the output load to sense the load current. The load current is fed to an instrumentation amplifier (INA) to measure the voltage drop across the shunt resistor and to feed it back to the input, thereby closing the control loop.
With this approach, which is widely used, to achieve good accuracy both the (shunt) resistor and the INA must have high accuracy and low drift. This leads to additional cost and board space. Furthermore, the voltage drop across the shunt resistor reduces the voltage headroom to the load and the power efficiency. In addition, the range of the current for an accurate output is limited. For small current levels through the shunt resistor, errors of the INA dominate; whereas, for large current levels, the voltage headroom and power efficiency to the load are reduced. As the potential at the load can change significantly, the INA must have a high common mode rejection which requires a trim of the common mode rejection ratio (CMRR). Finally, due to multiple stages of the feedback loop, an additional compensation is necessary. This requires the application to be overcompensated, which leads to a reduced performance.